'So what is it then, Scientology?' asks a contractor delivering supplies to builders who were putting the finishing touches yesterday to Number 146, Queen Victoria Street, one of the City of London's most exclusive addresses.

'I mean,' continues the contractor , 'I've heard a lot about it. Is it based on science? Who's the big man in charge?'

Such questions are likely to be asked more often from today when the controversial Church of Scientology opens its biggest UK centre in a red-carpet bash likely to be attended by some famous followers, who include Tom Cruise, Juliet Lewis and John Travolta.

The building, a former bible centre, cost the church £23m to buy and millions of pounds more to refit and is a testament to the organisation's growing financial strength. From its marble floors to its towering stucco-clad arches, Scientology's latest centre - all 50,000 square foot of it - screams wealth.

'I have always thought there might be a lot of cash in starting a new religion,' George Orwell wrote in 1938. Scientology appears a text book example. Little more than 50 years old it claims to be the world's fastest growing religion with 10 million followers, all of whom pay to study its teachings. In the UK alone it claims to have 123,000 registered followers. Last year it opened 1,300 new missions around the world. In the last few years it has opened palatial centres in New York, San Francisco and Madrid.

The location of its new London centre, in the centre of high finance, suggests it might find a receptive audience.

'One of the big problems in the City is the subject of ethics and morals,' said church spokeswoman Janet Laveau. 'There are also problems with drugs and stress. The Way to Happiness [a key Scientology text] can show them how to handle this and do the right thing.'

It is hard, however, to locate the source of Scientology's apparent appeal, one which now appears to have intrigued Victoria Beckham, who said recently that she has discussed it with her new best friend, Katie Holmes, aka Mrs Tom Cruise.

On the walls of 146 Queen Victoria Street are stencilled the thoughts of the church's founder, L Ron Hubbard, a former detective and science fiction writer who developed Scientology in England during the Fifties and turned it into an organisation of bewildering complexity and power - and the target of a long-running FBI investigation.

'Man is basically good and it is this basic goodness we want to set free,' proclaims one stencilled aphorism. 'The purpose of the mind is to solve problems relative to survival,' runs another. So far so innocuous. As you walk around, though, the statements are more exotic. Slogans talk about the 'gift of immortality' and interactive TV screens explain something called the 'condition of affluence'. There are saunas and treadmills, so followers can 'purify' themselves.

And there are rows and rows of teddy bears, on which followers practise their Scientology skills before employing them on humans. And emeters: electronic devices that, in the hands of a Scientology 'auditor' - someone who has completed a number of the church's courses - can apparently detect a person's mood swings. It is the stuff of Star Trek, all carried out in rooms whose walls are bedecked with pictures of Hubbard. As with every Scientology centre, Hubbard, who died in 1986, has his own room, which cannot be entered by others.

To the outsider it's baffling stuff, but Scientology maintains it can help its followers transform their lives. It makes impressive - and difficult to verify - claims that its courses can get people off drugs and reduce recidivism. It does much, ostensibly laudable work, promoting human rights, and its volunteers can be found helping at the scenes of major disasters, such as the 7 July bombings.

If Cruise or any other celebrities turn up tomorrow as expected it is because they believe Scientology has helped them climb the Hollywood ladder. 'Anti-social types will often try to leech off the success of creative types,' Laveau says. 'Scientology allows people to deal with them. It's about empowerment.'